The present invention relates to a vacuum pump. Specifically, the present invention relates to a vacuum pump which is a composite turbo molecular pump with a thread groove type pump portion in which a space (gap, clearance) between a stator portion and a rotary portion on the lower side of a thread groove portion can be changed.
Among all various vacuum pumps, turbo molecular pumps and thread groove type pumps are greatly used for realizing a high vacuum environment.
A chamber for semiconductor manufacturing equipment, a test chamber of an electron microscope, a surface analysis device, a microfabrication device, and the like are used as vacuum apparatuses, the insides of which are maintained vacuum through an exhaust process using a vacuum pump such as a turbo molecular pump or a thread groove type pump.
Such a vacuum pump for realizing a high vacuum environment has a casing that configures a casing having an inlet port and an outlet port. A structure that exerts an exhaust function of the vacuum pump is accommodated in this casing. The structure exerting an exhaust function is basically configured by a rotary portion (rotor portion) that is supported rotatably and a stator portion that is fixed to the casing.
In case of a turbo molecular pump, a rotary portion has a a rotating shaft and a rotary body fixed to the rotating shaft, wherein the rotary body has a plurality of stages of rotor blades (moving blades) arranged radially. The stator portion has a plurality of stages of stator blades (stationary blades) arranged alternately with respect to the rotor blades.
The turbo molecular pump is also provided with a motor for rotating the rotating shaft at high speed. When the rotary shaft is rotated at high speed by the operation of the motor, gas is drawn through the inlet port by the interaction between the rotor blades and the stator blades and discharged from the outlet port.
Incidentally, in such vacuum pumps as these turbo molecular pumps and thread groove type pumps, exhaust gas that includes microparticles of a reaction product generated in, for example, a chamber for semiconductor manufacturing equipment or other particles (e.g., particles of several μ to several hundred μm) generated in a vacuum container, is taken in through the inlet port.
Depending on the processes performed by the vacuum apparatus disposed in the vacuum pump, the suspended matters called particles inevitably adheres to the inside of the vacuum pump as products (deposits). Exhaust gas that is discharged in this manner, too, might be solidified into products in response to a sublimation curve (vapor pressure curve). Such products are often deposited and solidified especially in the vicinity of the outlet port where the pressure of the gas is high.
A gas passage becomes narrow and back pressure increases as the deposition of the products proceeds in the vicinity of the outlet port. As a result, the exhaust performance of the vacuum pump deteriorates significantly.
In addition, the rotary body of the vacuum pump is made of metal such as aluminum alloy and normally rotates at 20000 rpm to 90000 rpm. The peripheral velocity of the tips of the rotor blades reaches 200 m/s to 400 m/s. This consequently causes a phenomenon called “creep” where the rotor portion (especially the rotor blades) of the vacuum pump expands thermally or becomes distorted in a radial direction over the course of operating time. Because the thermal expansion or creep phenomenon of the vacuum pump occur more significantly on the lower side (outlet port side) of the rotary body than on the upper side (inlet port side) of the same, the expanded rotary body and the deposited products might come into contact with each other especially on the outlet port side.
Moreover, in a case where the apparatus disposed in the vacuum pump is a chamber for semiconductor manufacturing equipment, since the main raw material of a wafer used for manufacturing a semiconductor is silicon, the deposited products are harder than the rotary body made of aluminum alloy. When such products come into contact with the rotary body rotating at high speed as described above, the rotary body with lower hardness breaks, and, in the worst case, the functions of the vacuum pump stop.
Because such a vacuum pump has a problem in which a part of the vacuum pump comes into contact with products deposited in the vicinity of the outlet port where the pressure/temperature of the gas is high, which deteriorates the performance of the vacuum pump and breaks the rotor blades, an overhaul for disassembling the apparatus and carefully cleaning the same needs to be performed on a regular basis in order to remove the adhered products.
There has been conventionally proposed a technology for adjusting a space (clearance) between a rotor and a stationary wall from the outside of a casing, for the purpose of coping with the creep phenomenon described above.
Japanese Patent Application Publication No. 2003-286992 discloses a turbo molecular pump in which a casing thereof is provided with an axial flow stage portion configured by moving blades and stationary blades, and a thread groove stage portion configured by a thread groove rotor portion and a seal ring, wherein a minimum space is secured between the thread groove rotor portion and the seal ring. This turbo molecular pump is provided with space adjusting means for forming sections facing each other in a radial direction with the space therebetween into a tapered shape and adjusting the space by moving the seal ring from the outside of the casing in an axial direction.
According to this configuration in which the thread groove rotor portion and the seal ring are relatively moved in the axial direction, the rotor of the turbo molecular pump is prevented from being deformed and coming into contact with the stationary wall (seal ring), by adjusting/managing the size of the space between the thread groove rotor portion and the seal ring. In this manner, the operating life of the turbo molecular pump is extended.
In Japanese Patent Application Publication No. 2003-286992, however, the space between the thread groove rotor portion and the seal ring is adjusted based on the configuration in which the thread groove rotor portion and the seal ring are relatively moved over the entire surface of the thread groove rotor portion in the axial direction, resulting in expanding the space between the thread groove rotor portion and the seal ring, including the portions that do not require any adjustments (i.e., the upper side of the thread groove rotor portion; the section on the outlet port side).
However, as described above, the products are likely to be deposited in the section where the pressure of the gas is high (e.g., the lower side of the thread groove spacer of the thread groove type pump portion). Therefore, as disclosed in Japanese Patent Application Publication No. 2003-286992, if the thread groove rotor portion and the seal ring are relatively moved over the entire surface of the thread groove rotor portion in the axial direction with the purpose of expanding a space where the products deposit, the space is expanded at a constant interval in the axial direction, resulting in expanding a space in a section where the products rarely deposit (e.g., the upper side of the thread groove spacer of the thread groove type pump portion). This might deteriorate the performance of the vacuum pump more than necessary.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.